Voltage tunable Gunn effect semiconductor for microwave generatio

Rindner, W.

Roth, H.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
November 6, 1970 REPLY TO 
ATTN OF: G p  
~ ~ ~ / ~ c i e n t i f i c  & Technical Information Division 
Atcontion% M i s s  Winnle M. Morgan 
~ ~ / 0 f f i c e  of Assi?tapt General Counsel for  
Patent Matters 
* 
SUBJECT: Announcement of NASA-Owned U. S, Patents i n  STAR 
In accordance with the procedures agreed upon by Code G P  
and Code U S I ,  the attached NASA-awned U. S .' Patent is 'hing 
forwarded fo r  abstracting and announcement i n  NASA STAIR, 
, . 
The following information is providedr 
U. S. Patent No. 
Government or 
Corporate Employee 
Supplementary Corporate 
Source ( i f  applicable) 
NASA Patent Case N y  . 
NOTE - I f ' t h i s  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is a2plicable: 
yes 0 NO H 
Pursuant t o  Section 305(a) of the National Aeronautics and 
Space Act, the name of the Administr.ator of NASA appears on 
the f i r s t  page of the patent; however, the name of the actual 
inventor (author) appears a t  the heading of Column No. 1 oE 
-. - 
- - 
Elizabeth A. Carter 
~nc losure  
Copy of Patent a i ted  &we a 
2 
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2 (NASA CR OR TMX OR AD NUMBER) 
Y 
https://ntrs.nasa.gov/search.jsp?R=19710009246 2020-03-17T02:47:28+00:00Z
April 28, 1970 w. R I N B N E I  E T A L  3,509,49 1 
VOLTAGE-TUNABLE G U N N - T Y P E  idiCR0WAV.E GbNLRATOR 
Kiied J u n e  2, 196'7 
lNVENTORS 
W I! helm Rindner 8 
F I G . 4 -  Harold ~ o j h  
hY5 
United States Patent 8fi ce patented .PF. 3,509,491 28, 1970
- . . - -  
1 2 
a numb,er of Gunn generators must be created and 
3,503,491 checked to determine their frequency of operation. Sub- VBLThGE-TUNWBLE GUI".IN-TyEE MECRBBWAVE sequently, those that operate at the desired frequencies GENERATOR are chosen. This method of obtaining a Gunn generator, Wilhelilll Wiiadner, Lexingtail, and Barold Roth, Needham, inter alia, increases the cost of the device. Mess., assigrzors to Lhe United States of America as 5 
represented by the Administrator of the National Aero- Therefore, it is an object of this invention to provide 
raautisa agid Space Administration a new and improved semiconductor device that is fre- 
W'ed June 2,1967, Ser. No. 644,444 quency stable but generates signals of different frequen- 
Int. 61. H Q 3 b 7 / 1 4 , 1 1  / l o ,  15/00 cies over a range of frequencies. 
U.B. @I. 331-187 6 Claims: J t  is also an object of this invention to provide a new 
and improved Gunn generator that generates a signal 
ABSTRACT OF THE DISCLOSURE 
having a frequency related to the voltage applied to its 
contacts. 
In one embodiment, a Gunn-effect semiconductor chip It is still another object of this invention to provide 
having a varying cross-sectional area is mounted between 15 a new and improved Gunn generator that generates sig- 
a pair of contacts. An electric field gradient exists along nals over a frequency range. 
the current axis of the chip when a voltage is applied It is still another object of this invention to provide 
to the contacts. This electric field in conibination with a new and improved Gunn semiconductor microwave 
the variation in cross-sectional area causes the generated generator. 
frequency to vary in accordane with the applied volt- 20 
age when the voltage is above the critical Gunn level for SUMMARY OF THE INVENTION 
a portion of the current axis. That is, a variation in the 
applied voltage varies the length of the portioll of the In accordance with one embodiment of the invention, 
field abo\ie the threshold level to vary the freqllency of a new and improved Gunn-type semiconductor gel~erator 
the output signal. In an alternate enlbodinlent, the elec- 25 is provided by creating an electric field gradient above 
tric field g,-adient is created by non.uniform doping of the threshold level along only a portion of the current 
the semiconductor block. axis between the contacts of the device. Therefore, whcn 
the voltage creating the electric field gradient varies, the 
length of tile field above the threshold level varies, to 
The invention described hereill was made by en~ploy~es  30 cause the frequency generated by the Gunn generator 
of the United States Government and may be manufac- lo vary. 
tured and used by or for the Govern~lleilt for govern- In accordance with a further principle of the inven- 
mental purposes wiihout the psylnellt of any royalties tion, an electric field gradient, wherein only a portion 
thereon or therefor. of the field is above the threshold level, is created by 
35 physically varying the cross-sectional area of the semi- 
BACKGROUND OF THE INVENTION conductor chip between the contacts. That is, the cross- 
Oile of the recently developed devices in the rapidly sectional area along the current axis of the chip is varied 
evolving szmiconducior field is the Gunn microwave gen- SO that when a voltage is applied to the contacts, an 
erator. This device is described in an article entitled electric field above the threshold potential is created 
"Instabilities of Current in 111-V Semiconductors" by 40 along only a portion of the current axis. 
J. B. Gunn, published in the IBM Journal of Research In accordance with a still further principIe of the in- 
and Developn~ent for April 1964, pp. 141-159. vention, the electric field gradient is created by varying 
Generally, the Gunn generator conlprises a fiat rectan- the doping of the chip between the contacts. This varia- 
gular or cylindrical chip of a hon~ogeneous semiconduc- tion in doping creates the same effect as the physical 
tor material. Usualiy the semiconductor is a conlbina- 45 cross-sectional change described in the preceding para- 
tion of elznlents from Group 111-V of the Periodic Table graph. That is, when the voltage applied to the contacts 
such as galium arsenide or indium phosphide, for ex- varies, the electric field along the current axis that is 
ample. Contacts are applied to the two end faces of the above the threshold level varies, to vary the f r e q ~ l e n c ~  
chip. of the generated signal. 
In op-ration, a vokage is applied to the chip whizh 50 Varying either the cross-sectional area or the doping 
creates an electric field across th? When the elec- of a conventional Gunn generator creates a variable 
tric field reaches a critical value known as the threshold frequency generator that is geonletrically small, com- 
level fr., the device generates an output signal of a stable pact and reliable. These changes provide a device whose 
frequency. That is, the applied voltage creates an electric output freqrlency can be easily controlled by controlling 
field across the semiconductor chip and wllm this volt- 55 the bias voltage applied to the device. The device does 
age level reaches a threshold or critical val~ie the output net have 10 be designed to generate a particular fre- 
signal froIn the device is frequency constant. The voltage quency as with prior art devices, since merely controlling 
may rise above the threshold level but the frequency the voltage applied to the device creates a signal of the 
remains coiistant. The actuzl frequency of the signal is desired frequency. Hence, the device is useful, for ex- 
d,-tel-mined by the disiancs between the contacts. 60 ample, as a voltage corrtroiled oscillator, as a modulator, 
Wl-iile the Gunn device as desci.ibed ;:bow and in the etc. 
forzgoing article is a substnntial step forivard in the BRIEF DESCRIPTION OF THE DRAWINGS 
art  becaiise it is georrieiricaliy smail, coiilpnci and re- 
liable, it ! ~ c s  cel-tain limitations. For example, becatlse The foregoing objects and many of the attendant ad- 
this prior art device is 1imi:ed to a specific frequency 65 vantages of this invention will become more readily ap- 
determined by the distance between the contacts, it lacks preciated as the same becomes better understood by 
versatility. That, is ir can only operate at a particular reference to the following detailed description when 
f ~ . ~ ~ ~ ~ e ~ l c y  and not over a fi-eqi~ency range, as is desirable taken in conjunction with the accompanying drawings 
in many environnients. Further, because of the physical wherein: 
problems of creating a particular separaticn between thc 70 FIG. 1 is an illustration of one embodiment of the 
col~tacts, it is extremely diffic~ilt to create a device that invention utlizing a chip of uniformly decreasing (or 
operates at a specific predetermined frequency. Rather, increasing) varying cross-section; 
3 4 
FIG. 2 is an illustration of an alternative embodiment FIG. 2, illustrates a further alternative embodiil-~eni 
of the invention employing a doped configuration; and of the iclvention that cornpi-ises a semicoodr~ctor chip 38 
FIGS. 3 and 4 are further variations of the FIG. 1 having a first surface 33 and a second sr11-face 35. A first 
embodimeilt but utilize chips of non-uniform varying tcrlr~irlal 37 is connected to :Iic first slirfacc 33 by a con- 
cross-section. ductor 39 and a s~cond terminal 41 is connected to the 5 second surface 35 by a cond~~ctor 43. The terminals 37 
DESCRIPTION OF THE PREFERRED and 41 are connected to the positive and negative side, 
EMBODIMENTS respectively, of the voltage source. The embodiment il- 
prior art G~~~ devices are formed of flat rectangular lustrated in FIG. 2 has a substantially constant cylindrical 
or circular ,-hips of G~~~~ 111-v semiconductor cross-section between the first and second surfaces. Hence, 
pounds such as gallium arsenide or indium phosph;de, this configuration is similar to a conventional Gunn 
for example. A pair of contacts are attached to the paral- device. 
lei, fiat surfaces. l-he ,.hip has 'both uniform cross- While the configuration of the embodiment illustrated 
sectional area uniform doping; for example, the chip in FIG. 2 is similar to a conventional Gunn device, the 
may be doped with tellurium to give it ~ - t ~ ~ ~  properties. 15 doping is not. That is, whereas in prior art Gunn devices 
For operation, the device requires that a minimum the doping between the first and second surfaces was 
threshold electric field be created along the current axis unifornl, the doping between the first and second surfaces 
of the device. This electric field is created by applying of FIG. 2 is varied. More specifically, the doping near 
an electric potential across the contacts. When the elec- the first surface 33 may be higher (illustrated as N f )  
tric field exceeds the threshold level, the device generates 20 than the doping near the second surface 35 (illustrated as 
a stable microwave signal at a frequency determined by N). This variation in doping provides a similar effect as 
the distance between the two contacts. the physical cross-sectional variations illustrated in the 
This invention improves upon the prior art devices other figures. That is, the variation in doping between 
by creating a device wherein the electric field gradient the first and second surfaces 33 and 35 creates a device 
along the current axis of the device is such that the 25 wherein only a portion of the electric field gradient along 
threshold level only exists along a portion of the axis. the current axis is above the threshold level for a par- 
When the applied voltage that creates the electric field ticular bias voltage. Hence, a stable output signal fre- 
varies, it varies the portion of the electric field that is quency is achieved. And, when the bias voltage is varied 
above the threshold level to  vary the frequency of the the portion of the electric field above the threshold level 
generated signal. FIGS. 1, 2, 3 and 4 illustrate embodi- 30 varies to vary the output signal frequency. As described 
ments of the invention made in accordance with the con- with respect to FIG. 1, the device can operate, for exam- 
cept of the invention. It should be noted that these ple! as a voltage-controileti oscillator or as a modulator. 
figures are longitudinally distorted to  better illustrate It 1s to be understood that the fields necessary to sustain 
the inventive concept. the Gunn-type oscillations and the field levels at which 
The embodiment of the invention illustrated in FIG. 35 the domains are extinguished are given by conventional 
1 comprises a chip of semiconductor material 11, a first Gunn effect theory as described in the aforecited article 
contact surface 13 and a second contact surface 15. A by J .  B. Gunn. Namely, nucleation commences in regions 
terminal 17 is connected by a conductor, 19 to the first of the highest field. For example, in FIGURES 1, 3, and 
contact surface 13 and a terminal 21 is connected by a 4, nucleation starts where the cross-section is smallest- 
conductor 23 to the second surface 15. The embodiment 40 which is where the field is the highest. And in FIGURE 
illustrated in FIG. 1 is in the form of a truncated-cone 2, nucleation starts where the doping is the least-which 
having the first surface diameter D l  larger than the is where the field is highest. Extinction is in that part if 
second surface diameter D2; hence, the cross-sectional the device away from the cathode where the electric field 
area between the two surfaces varies along the current is inadequate to sustain Gunn domains. 
axis of the device. The surfaces 13 and 15 may be parallel qj  xt will be appreciated by those skilled in the art and 
to each other. It is this variation in cross-sectional area others that the embodiments of the invention illustrated 
that provides the unique results of the invention. in FIGS. 1, 2 and 3 are only by way of example. In gen- 
Preferably, the semiconductor chip 11 is formed of eral, what is required with respect to the type of embodi- 
a Group 111-V semiconductor compound that is appro- ment illustrated in FIGS. 1, 3 and 4 is that the device 
priately doped to create an N-type device. 50 have a varying cross-sectional area between the two sur- 
In operation, a potential from a voltage supply 1% is faces. For example, the device could be a square-or rec- 
applied between terminal 17 and 21 to create an electric tangular-shaped chip having a pair of surfaces with a 
field gradient between the surfaces 13 and 15. The termi- varying cross-sectional area between the surfaces. 
nals 17 and 21 are connected to the positive and negative It will be further appreciated by those skilled in the 
slde, respectively, of the voltage source. The potential 55 art that the means for creating the electric field gradient 
must be large enough to create an electric field above illustrated in the figures could be combined. That is, both 
the threshold level along a portion of the current axis the cross-sectional zrea effect and the variation in doping 
between the contacts. When this threshold level is reached, effect could be used to create an overall effect in a com- 
the output signal across the same terminals 1'7 and 21 bined device. In this manner the overall device would 
is at a first frequency. By further increasing the potential 60 have benefits. 
or hias across the terminals 1'7 and 21 the frequency Eence, the i ~ ~ v ~ n t i o n  may be practiced otherwise than 
of the output signal on these terminals changes. Hence, as described herein. 
the device is a voltage-controlled oscillator. That is, What is claimed is: 
as the applied voltage changes the outpirt frequency I. A sernicond~lcior variable frequency Gi~nn-ei'iect 
changes. Further, the device can be rised as a moclu:ator 65 o.,cillator. enabiinE conlinllolrs eleclrorric of t!lr, in that when the appliecl voltage is moduiated the output 
output frequency comprising: frequency is modulated. 
FIGS. 3 and 4 illustrate embodiments of the invention a chip of Gunn-effect semicondl~ctor material forming 
that are similar to FIG. 1 illustration except that the chips a truncated cone between a pair of opposed surfaces; 
l1n and I l b  have no uniform varying cross-sections. 70 and 
For example, at 4'7 in FIG. 3, the surface of the chip means forming a pait of said chip and associated with 
I ln  changes abrtiotlv. Similarlv, in FIG. 4, the surfaces said suifaces for applying a potential to create an 
of chip f1b mayLbe" exponent&l, or the like. It will be electric field gradient between said surfaces to cause 
noted that similar reference numerals denote like parts said device to genelate a signal whose frequency is 
in FIGS 1, 3 and 4. 75 dependent upon the amplitude of the potential. 
3,509,491 
5 6 
2. A device as c!airiled in ciairn 1 wirerein saiii chip 5. A device as cli~irneil in claim 4 wherein said chip is 
is formed of gallium arsenicie. formed of gallium arsenide. 
3 .  A elevice as claimed in claim 1 wilercin said chip 6. A tievice as c!airnecl in claim 4 wherein ssiti chip 
i s  formed of' inciium pftc.;phit!e. is fori-!led of indium phospliide. 
4. A sen~icoilducior variable frequency Gunn-effect os- 5 
cillator enabling continuous electronic control of the out- References Cited 
put frequency comprising: UNITED STATES PATENTS 
a chip of Gunn-effect semiconductor material having 3,365,583 Gunn ------------ 33  1 - 1 ~ 7  x 
a  air of opposed surfaces, the material between 3,377,566 4/1968 Lanza -------------- 331-107 
said surfaces containing varying doping concentra- 10 
tions and having varying cross-sectional areas; and ROY LAICE, Primary Examiner 
means forming a part of said chip and associated with S. H. GRIMM, Examiner 
said surfaces for applying a potential to create an 
electric field gradient between said surfaces to cause U.S. Cl. X.R. 
said device to generate a signal whose frequency is l5 
dependent upon the amplitude of the potential. 307-322; 317-235 


Voltage tunable Gunn-type microwave generator Patent

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